A device for a downhole apparatus for machining of casings is described, more particularly a device arranged to direct machined shavings in a direction from a machining area toward the end portion of a well bore by means of a flowing well liquid, and to thereafter direct the well liquid to a surface installation. A method for depositing machined shavings in the well bore is also described.
When a well such as a hydro carbon producing well is to be shut in, there has to be established a plug such as a cement plug, according to public safety regulations and common practice, in the well bore above, i.e. downstream of the producing zone, as the plug has to be anchored in the structure above the producing zone. This implies among other things that portions of a metal casing extending through the well are removed where the plug is to be established. Such removal is done by means of machining of the casing from the inside of the pipe. In prior art the metal shavings from the mechanical machining are transported by means of flowing well liquid from the underground up to the surface where mechanical equipment is used to separate the metal shavings from the well liquid. Metal shavings are collected and brought to a treatment plant where they are cleaned of liquid remnants and used for example in the production of new metal products. The remaining products from the cleaning process, i.e. well liquid remnants and any cleaning liquid used, must be treated as hazardous waste.
The metal shavings removed from the casing are directed with the well liquid through pipe paths such as an annulus outside a feed pipe for the well liquid. There is a risk of the return path being blocked as a result of the metal shavings easily getting stuck in the flow path, or that the flow rate of the well liquid in the return pipe is too small compared with the rate of descent of the metal shavings. For that reason high flow rates are normally used requiring hydraulic pumps having very large power and correspondingly large mass and power consumption. In such operations, being mainly arranged for plugging and abandoning subsurface wells, it is a drawback that the pumping equipment is relatively heavy and power demanding compared to the rest of the equipment used. The equipment becomes less mobile and sets limitations, for example in transfer between ship and platform in work on sub-sea wells.